Magnetic-inertial global positioning system

1. A magnetic-inertial global positioning system mounted on a platform, the global positioning system comprising: an inertial system configured to determine an approximate latitude associated with an approximate global position of the platform; a magnetometer system configured to determine an ambient magnetic field at the approximate global position, the magnetometer system being further configured to determine the ambient magnetic field during motion of the platform along a motion trajectory; and a location processor configured to compare the ambient magnetic field with a predetermined magnetic field profile to determine an approximate longitude along the determined approximate latitude to determine the approximate global position of the platform the location processor being further configured to refine the approximate global position based on comparing the determined ambient magnetic field along the motion trajectory with the predetermined magnetic field profile.

2. The system of claim 1 , wherein the inertial system comprises: an accelerometer configured to determine a down vector associated with a gravity center of a celestial body associated with the approximate global position; and a gyroscope system configured to determine a net rotation of the platform about a spin axis of the celestial body; wherein the location processor is configured to determine the approximate latitude based on the down vector and the net rotation of the platform.

3. The system of claim 2 , wherein the accelerometer system comprises a plurality of accelerometers associated with each of three orthogonal axes that are configured to collectively determine the down vector, wherein the gyroscope system comprises a plurality of gyroscopes associated with each of three orthogonal axes that are configured to collectively determine the net rotation of the platform.

4. The system of claim 1 , wherein the location processor is configured to initially determine the approximate latitude in a range of uncertainty and is further configured to evaluate the ambient magnetic field with the predetermined magnetic field profile in the range of uncertainty of the approximate latitude to determine the approximate longitude.

5. The system of claim 1 , wherein the predetermined magnetic field profile is a predetermined latitude magnetic field profile that comprises magnetic field component values in each of three orthogonal axes along a 360° profile of the approximate latitude, wherein the location processor is configured to compare the ambient magnetic field along the predetermined latitude magnetic field profile to determine the approximate longitude associated with the approximate global position.

6. The system of claim 1 , further comprising a celestial tracking system configured to perform at least one stellar observation relative to the approximate global position, wherein the location processor is further configured to determine an approximate present time based on the at least one stellar observation.

7. The system of claim 6 , further comprising an internal clock configured to provide an initial time estimate, wherein the location processor is further configured to refine the initial time estimate in response to the at least one stellar observation.

8. The system of claim 1 , wherein the platform comprises a vehicle, wherein the inertial system is configured to determine the approximate latitude while the vehicle remains stationary at an initial location, wherein the inertial system is further configured to collect inertial data during motion of the vehicle from the initial location to generate navigation data, wherein the motion trajectory is determined based on the navigation data.

9. The system of claim 8 , further comprising a celestial tracking system configured to perform a first stellar observation at a first location prior to the motion and to perform a second stellar observation at a second location subsequent to the motion to determine an approximate present time based on the first and second stellar observations.

10. A magnetic-inertial global positioning system mounted on a platform, the global positioning system comprising: an inertial system configured to determine an approximate latitude associated with an approximate global position of the platform; a magnetometer system configured to determine an ambient magnetic field at the approximate global position; a magnetic model database configured to store a global magnetic field map of a celestial body associated with the approximate global position, the global magnetic field map comprising a predetermined magnetic field profile; a location processor configured to implement a matching algorithm to compare the determined ambient magnetic field with the predetermined magnetic field profile to determine an approximate longitude along the determined approximate latitude to determine the approximate global position.

11. A method for determining an approximate global position of a platform, the method comprising: determining an approximate latitude associated with an approximate global position of the platform via an inertial system associated with the platform; determining an ambient magnetic field at the approximate global position and along a motion trajectory via a magnetometer system associated with the platform; accessing a predetermined magnetic field profile from a memory associated with the platform; comparing the ambient magnetic field with the predetermined magnetic field profile to determine an approximate longitude along the determined approximate latitude to determine the approximate global position of the platform; and refining the approximate global position based on comparing the determined ambient magnetic field along the motion trajectory with the predetermined magnetic field profile.

12. The method of claim 11 , wherein determining the approximate latitude comprises: determine a down vector associated with a gravity center of a celestial body associated with the approximate global position via a plurality of accelerometers associated with each of three orthogonal axes; and determine a net rotation of the platform about a spin axis of the celestial body via a plurality of gyroscopes associated with each of the three orthogonal axes.

13. The method of claim 11 , wherein determining the approximate latitude comprises initially determining the approximate latitude in a range of uncertainty, wherein comparing the ambient magnetic field comprises evaluating the ambient magnetic field with the predetermined magnetic field profile in the range of uncertainty of the approximate latitude to determine the approximate longitude.

14. The method of claim 11 , wherein accessing the predetermined magnetic field profile comprises accessing a predetermined latitude magnetic field profile that comprises magnetic field component values in each of three orthogonal axes along a 360° profile of the approximate latitude, wherein comparing the ambient magnetic field comprises comparing the ambient magnetic field along the predetermined latitude magnetic field profile to determine the approximate longitude associated with the approximate global position.

15. A method for determining an approximate global position of a platform, the method comprising: determining an approximate latitude associated with an approximate global position of the platform via an inertial system associated with the platform; determining an ambient magnetic field at the approximate global position via a magnetometer system associated with the platform; determining an initial time estimate via an internal clock associated with the platform; accessing a predetermined magnetic field profile from a memory associated with the platform; comparing the ambient magnetic field with the predetermined magnetic field profile to determine an approximate longitude along the determined approximate latitude to determine the approximate global position of the platform; performing at least one stellar observation relative to the approximate global position via a celestial tracking system associated with the platform; and, refining the initial time estimate in response to the at least one stellar observation.

16. The method of claim 11 , wherein the platform comprises a vehicle, wherein determining the approximate latitude comprises determining the approximate latitude while the vehicle remains stationary at an initial location, the method further comprising: collecting inertial data during motion of the vehicle from the initial location to a second location to generate navigation data; and determining the motion along the motion trajectory from the initial location to the second location based on the navigation data.

17. A magnetic-inertial global positioning system mounted on a vehicular platform, the magnetic-inertial global positioning system comprising: an inertial system comprising: a plurality of accelerometers associated with each of three orthogonal axes that are configured to collectively determine a down vector associated with a gravity center of a celestial body and track a down vector direction along a motion trajectory between an initial location and a second location of motion of the vehicular platform; and a plurality of gyroscopes associated with each of three orthogonal axes that are configured to collectively determine a net rotation of the vehicular platform about a spin axis of the celestial body and to track a spin axis direction between the initial location and the second location of motion of the vehicular platform, the inertial system being configured to determine an approximate latitude of the vehicular platform in response to the down vector and the net rotation of the vehicular platform between the initial location and the second location; a magnetometer system configured to track an ambient magnetic field during the motion along a motion trajectory; and a location processor configured to compare the ambient magnetic field with a predetermined magnetic field profile to determine an approximate longitude along the determined approximate latitude to determine the approximate global position of the vehicular platform at the initial location and to continue to compare the ambient magnetic field with the predetermined magnetic field profile along the motion trajectory to refine the determination of the approximate global position at the second location.

18. The system of claim 17 , wherein the predetermined magnetic field profile is a predetermined latitude magnetic field profile that comprises magnetic field component values in each of three orthogonal axes along a 360° profile of the approximate latitude, wherein the location processor is configured to compare the ambient magnetic field along the predetermined latitude magnetic field profile to determine the approximate longitude associated with the approximate global position.

19. The system of claim 17 , further comprising: an internal clock configured to provide an initial time estimate; and a celestial tracking system configured to perform at least one stellar observation relative to the approximate global position, wherein the location processor is further configured to determine an approximate present time based on the initial time estimate and the at least one stellar observation.

20. The system of claim 17 , further comprising a magnetic model database configured to store a global magnetic field map of the celestial body, the global magnetic field map comprising the predetermined magnetic field profile, wherein the location processor is configured to implement a matching algorithm to compare the determined ambient magnetic field with the predetermined magnetic field profile to determine the approximate global position.